1. Field of the Invention
The present invention relates to a method for manufacturing a pattern formed body in which liquid is discharged and adhered onto a substrate by applying a voltage.
2. Description of the Related Art
A method, in which liquid is discharged from a nozzle like or slit like discharge orifice onto a substrate and is adhered, is used widely for graphics or various kinds of markings. As an example of such a method, the ink jet method, the dispenser method, or the like can be presented. These methods are advantageous in that the apparatus is simple, the cost of the material can be reduced, or the like compared with the conventional printing method or photolithography method. Recently, many attempts have been made for producing the members requiring minute patterning, such as a color filter for a liquid crystal display, by applying these methods.
The ink jet method is a method for forming a pattern by discharging and throwing small droplets of an ink from a minute discharge orifice so as to be adhered directly onto a substrate such as a paper. General principles for discharge are as follows: the piezoelectric system in which shape of the ink channel is changed by the vibration of a piezoelectric element so as to discharge an ink; and the thermal system in which bubbles are formed in an ink by the heat from a heat generating member in an ink channel and the ink is discharged by the pressure. In the ink jet method, development is executed vigorously for the purpose of making the liquid droplets smaller and stabilizing the landing of the liquid droplet. Nowadays, in the piezoelectric system ink jet method, the droplets small as 2 picoliters can be discharged.
However, as a serious problem of the ink jet method, only an extremely low viscosity ink of 50 cps or less viscosity can be discharged. Therefore, the solid component density in the ink cannot be made higher so that a plurality of liquid droplets are need to be superimposed in order to obtain a film thickness necessary in terms of the function. Moreover, the low viscosity ink is widely spread on the substrate surface after landing thereon, so that it has been problematic in terms of the fine pattern formation. Although a certain effect can be obtained by providing an ink absorbing layer on the surface of the substrate, it limits the field of application in not only the cost, but also in functions.
On the other hand, in the dispenser method, a high viscosity liquid can be discharged and adhered in lines or in dots. By making the inner diameter of the nozzle smaller, a narrower line or smaller dot can be discharged. Presently, a minute nozzle of about a 20 μm inner diameter is commercially available. Although it depends on the liquid viscosity, a minute patterning of about 30 μm is possible.
However, in the dispenser method, since liquid droplets smaller than the nozzle inner diameter cannot be discharged, the nozzle inner diameter always must be made smaller for a minute patterning. Therefore, for discharging a high viscosity liquid, an extremely high pressure must be applied. Moreover, particularly in the case of a high viscosity liquid, the gap between the nozzle and the substrate must be made smaller so that it is difficult to provide an apparatus so as to provide a cause of a problem.
Furthermore, as a common problem for the ink jet method and the dispenser method, in the both methods, since the nozzle inner diameter needs to be made smaller to the 10 μm order in order to discharge minute liquid droplets, an ink obtained by dispersing particles of large diameter, such as a fluorescent substance, a glass frit, a photoluminescent pigment, a magnetic substance, can hardly be discharged stably due to the problem of the clogging.
Accordingly, the present inventors have discussed the various aspects of a method for forming a minute pattern using an high viscosity ink or an ink including large particles so as to achieve the invention of the electric field jet method (for example, see Japanese Patent Application Laid-open (JP-A) Nos. 2000-246887 and No. 2002-126615). The electric field jet method is a method, in general, in which an ink is supplied to a discharge head having a nozzle like or slit like discharge orifice provided with electrodes in the vicinity thereof, and then, the ink is discharged continuously or intermittently from the discharge orifice by applying an alternating voltage or a direct voltage to the above-mentioned electrode.
In the electric field jet method, not only a high viscosity ink of several tens of thousand cps can be discharged like a dispenser, but a low viscosity ink of several cps or less can also be discharged as well. It is the largest characteristic of the electric field jet method that the tip diameter of the ink to be discharged can be made smaller than the nozzle inner diameter, owing to the electric field effect. Depending on the combination of the ink and the discharge head, the size of the line or the dot to be patterned can be made smaller to 1/10 or less of the nozzle inner diameter. Also, since the nozzle inner diameter can be made relatively large according to the objective pattern, an ink including large particles can be discharged stably with a high resolution without clogging.
However, since the electric field jet method is extremely sensitive to the influence of the substrate surface, even though stable discharge is possible on an even substrate such as a raw glass, in the case of a substrate with uneven surface or a substrate having a conductivity difference, it has been extremely difficult to land the ink on a desired position because of the act of a force to make the liquid land on the higher part of the unevenness or on a part of higher conductivity. Moreover, even though it can be improved by adjusting the conductivity of the liquid or by optimizing the applied voltage, it has its own limit so that the discharge onto a substrate with unevenness or the stable discharge onto a substrate already provided with a conductive pattern can hardly be achieved.